A conventional electrical system of a vehicle may include a wireless communication unit that is capable of wireless communication with a user's portable electronic device based on Bluetooth® protocol. Therefore, the user can access other electrical devices of the vehicle (e.g., an audio player, a speaker, etc.) via a wireless connection between the wireless communication unit and the portable electronic device, for example, for playing music files stored in the portable electronic device or for answering a phone call. However, when a main switch of the vehicle is switched to a non-conductive state, the electrical supply from a battery of the vehicle to the wireless communication unit is cut off, and accordingly, the wireless communication unit is unable to establish or maintain the wireless connection with the portable electronic device.